vs/sessions — Agentic Sessions Window Layer

Overview

The vs/sessions layer hosts the implementation of the Agentic Window, a dedicated workbench experience optimized for agent session workflows. This is a distinct top-level layer within the VS Code architecture, sitting alongside vs/workbench.

Architecture

Layering Rules

vs/base          ← Foundation utilities
vs/platform      ← Platform services
vs/editor        ← Text editor core
vs/workbench     ← Standard workbench
vs/sessions      ← Agentic window (this layer)

Key constraint: vs/sessions may import from vs/workbench (and all layers below it), but vs/workbench must never import from vs/sessions. This ensures the standard workbench remains independent of the agentic window implementation.

Allowed Dependencies

From `vs/sessions`	Can Import
`vs/base/**`	✅
`vs/platform/**`	✅
`vs/editor/**`	✅
`vs/workbench/**`	✅
`vs/sessions/**`	✅ (internal)

From `vs/workbench`	Can Import
`vs/sessions/**`	❌ Forbidden

Folder Structure

The vs/sessions layer follows the same layering conventions as vs/workbench:

src/vs/sessions/
├── README.md                           ← This specification
├── LAYOUT.md                           ← Layout specification for the agentic workbench
├── AI_CUSTOMIZATIONS.md                ← AI customization design document
├── sessions.common.main.ts             ← Common (browser + desktop) entry point
├── sessions.desktop.main.ts            ← Desktop entry point
├── common/                             ← Shared types and context keys
│   └── contextkeys.ts                  ← ChatBar context keys
├── browser/                            ← Core workbench implementation
│   ├── workbench.ts                    ← Main workbench layout (Workbench class)
│   ├── layoutActions.ts                ← Layout toggle actions
│   ├── menus.ts                        ← Menu IDs for agent sessions menus (Menus export)
│   ├── paneCompositePartService.ts     ← AgenticPaneCompositePartService
│   ├── style.css                       ← Layout styles
│   ├── widget/                         ← Agent sessions chat widget
│   │   ├── AGENTS_CHAT_WIDGET.md       ← Chat widget architecture documentation
│   │   ├── agentSessionsChatWidget.ts  ← Main chat widget wrapper
│   │   ├── agentSessionsChatTargetConfig.ts ← Target configuration (observable)
│   │   ├── agentSessionsTargetPickerActionItem.ts ← Target picker for input toolbar
│   │   └── media/
│   │       └── agentSessionsChatWidget.css
│   └── parts/                          ← Workbench part implementations
│       ├── titlebarPart.ts             ← Simplified titlebar part & title service
│       ├── sidebarPart.ts              ← Sidebar part (with footer)
│       ├── auxiliaryBarPart.ts         ← Auxiliary bar part (with run script dropdown)
│       ├── panelPart.ts               ← Panel part
│       ├── chatBarPart.ts             ← Chat bar part
│       ├── projectBarPart.ts          ← Project bar part (folder entries)
│       ├── parts.ts                   ← AgenticParts enum
│       ├── agentSessionsChatInputPart.ts  ← Chat input part adapter
│       ├── agentSessionsChatWelcomePart.ts ← Chat welcome part
│       └── media/                     ← Part CSS
├── electron-browser/                   ← Desktop-specific entry points
│   ├── sessions.main.ts
│   ├── sessions.ts
│   ├── sessions.html
│   └── sessions-dev.html
├── contrib/                            ← Feature contributions
│   ├── accountMenu/browser/            ← Account menu widget and sidebar footer
│   │   └── account.contribution.ts
│   ├── aiCustomizationManagement/      ← AI customization management editor
│   │   └── browser/
│   ├── aiCustomizationTreeView/        ← AI customization tree view sidebar
│   │   └── browser/
│   ├── changesView/browser/            ← File changes view
│   │   ├── changesView.contribution.ts
│   │   └── changesView.ts
│   ├── chat/browser/                   ← Chat-related actions and services
│   │   ├── chat.contribution.ts
│   │   ├── branchChatSessionAction.ts
│   │   ├── runScriptAction.ts
│   │   └── promptsService.ts
│   ├── configuration/browser/          ← Configuration contribution
│   │   └── configuration.contribution.ts
│   └── sessions/browser/              ← Sessions view and title bar widget
│       ├── sessions.contribution.ts
│       ├── sessionsViewPane.ts
│       ├── sessionsTitleBarWidget.ts
│       ├── activeSessionService.ts
│       └── media/

What is the Agentic Window?

The Agentic Window (Workbench) provides a simplified, fixed-layout workbench tailored for agent session workflows. Unlike the standard VS Code workbench:

Fixed layout — Part positions are not configurable via settings
Simplified chrome — No activity bar, no status bar, no banner
Chat-first UX — Chat bar is a primary part alongside sidebar and auxiliary bar
Modal editor — Editors appear as modal overlays rather than in the main grid
Session-aware titlebar — Titlebar shows active session with a session picker
Sidebar footer — Account widget and sign-in live in the sidebar footer

See LAYOUT.md for the detailed layout specification.

Adding New Functionality

When adding features to the agentic window:

Core workbench code (layout, parts, services) goes under browser/
Feature contributions (views, actions, editors) go under contrib/<featureName>/browser/
Register contributions by importing them in sessions.desktop.main.ts (or sessions.common.main.ts for browser-compatible code)
Do not add imports from vs/workbench back to vs/sessions
Contributions can import from vs/sessions/browser/ (core) and other vs/sessions/contrib/*/ modules
Update the layout spec (LAYOUT.md) for any layout changes